Combines are large self-propelled vehicles used for harvesting and threshing agricultural crop in a field. A combine operates by cutting or gathering crop standing in a field, and feeding the cut crop to a separator by means of a conveyor mechanism. In the separator, grain is threshed, or beaten from the husk, stems, pods, or cobs, and then the threshed grain is separated from crop material other than grain. After separating, some crop material other than grain is still mixed with the grain. A cleaning system is used to remove the crop material other than grain, sometimes called trash or chaff, from the grain. This is typically done in a device known as a cleaning shoe, which has mechanisms known as a chaffer and a sieve. Typically, the chaffer and sieve are large pans having a flat surface that are oscillated or vibrated to break up the crop material and separate out the grain. The chaffer and sieve can also be a series of adjacent planks that are oscillated or vibrated. The chaffer and sieve can be generally horizontally level from the front to back, or as is commonly seen, arranged to have an upward incline from front to back. In some cleaning systems, a fan is also used to blow the lighter chaff away from the heavier grain material in the chaffer and/or sieve.
In operation, the mixed grain and crop material is deposited onto the top front of the chaffer. The lighter weight chaff is separated from the grain by vibration and/or blowing, and the grain and small heavy particles of crop material other than grain fall through louvers in the floor of the chaffer onto the sieve, which is located beneath the chaffer. The sieve oscillates to separate out and break up crop material. The grain, which is heavier than the other crop material, falls through appropriate-size openings in the floor of the sieve, and the cleaned grain from the sieve is carried to the grain tank.
Because the cleaning shoe operates by shaking and/or blowing lighter material away from the heavier grain, cleaning shoes tend to work best on flat ground. When the combine is operated on a slope, the crop will tend to build up on the low side of the sieve and chaffer due to gravitational forces. This will result in inefficient cleaning action, with resultant grain loss.
While combines with pivoting wheel axles exist for use on land that is predominantly sloped, these hillside combine systems are complex and costly, and of a level of sophistication not needed for operation on generally flat ground or ground having only a mild degree of slope. Instead, one alternative solution for use with limited slope operation is for the level-land combines, as they are sometimes called, to utilize chaffers and sieves made from a plurality of adjacent longitudinal sections separated by dividers. When operating on a slope, material builds up against the dividers, which helps limit the crop build-up to just crop in that particular longitudinal section. However, these devices only reduce crop build-up on the downhill side of the combine, rather than completely eliminating the problem, resulting in cleaning that does not provide maximum grain yield, due to inefficient use of the cleaning shoe.
Additionally, some combines utilize systems in which the chaffer and/or sieve, or each longitudinal section thereof is pivotally mounted in a frame such that it can be pivoted or tilted relative to the frame to maintain the device level in relation to the slope of the combine and the ground. Such mechanisms are typically operated by means of an inclinometer and a motor to pivot the sections along their length with respect to the slope of the ground. Other mechanism utilize hanging weights tied into the pivots of the longitudinal sections to tilt the chaffer and/or sieve sections to horizontal and compensate for the slope of the combine. However, even with the use of systems that keep the chaffer or sieve sections horizontal relative to the ground slope, crop processing efficiency is decreased as compared to level-land processing, with efficiency losses depending on factors such as crop conditions and harvesting speed. Therefore, what is needed is a method and apparatus for crop harvesting on rolling or sloped ground that minimizes grain loss typically seen when harvesting on sloped ground, without having to reduce harvesting speed or utilize expensive mechanisms to achieve desired harvest yields.